In the broadcast audio/video environment, video and audio signals are typically represented in a digital manner. There are many transports which are used to move these signals between devices. One common such transport is known as SDI, or Serial Digital Interface, as specified by the Society of Motion Pictures and Television Engineers (SMPTE) and the International Telecommunications Union (ITU). This signal transport carries audio and video signals, in a serial bitstream, between devices over a variety of media, including coaxial cable or fiber optic cable.
The SDI standards can represent a wide variety of video standards, including National Television System Committee (NTSC), Phase Alternating Line (PAL), High Definition Television (HDTV—1080i, 720p, 1080p), or Ultra-High Definition Television (UHD−2160p). Depending upon the video standard being carried, the data rate of an SDI transport may vary among a number of pre-defined rates, ranging from 270 Mbit/s up to 12 Gbit/s.
Since SDI signals are transmitted on a single transmission line, without a forwarded clock, it is necessary for a device receiving an SDI signal to recover the clock from the incoming signal and to align the serial data stream for proper decoding.